如何修改Plotly图例：让符号覆盖标记并替换图例文本

需求说明 #

需要实现两个修改：

• 图例中的符号（+、-、?）覆盖在标记上方，而非标记之后
• 将图例文本替换为：increase（对应+）、decrease（对应-）、unknown（对应?）

修改后代码 #

library(plotly)

# 重构数据：分离类别与符号
df <- data.frame(
  x = 1:3,
  y = 0,
  category = c("unknown", "increase", "decrease"),
  symbol = c("?", "+", "-")
)

# 绘制主图，关闭默认图例
p <- plot_ly() |>
  add_trace(
    data = df,
    x = ~x,
    y = ~y,
    text = ~symbol,
    color = ~category,
    type = "scatter",
    mode = "markers+text",
    marker = list(size = 20),
    textfont = list(size = 12, color = "white"),
    textposition = "middle center",  # 让符号在标记正中央
    showlegend = FALSE  # 关闭默认图例，改用自定义图例
  )

# 添加自定义图例（通过annotations实现精确控制）
p |> layout(
  annotations = list(
    # unknown项
    list(
      x = 1.02, y = 0.5, xref = "paper", yref = "paper",
      text = "unknown", showarrow = FALSE,
      xanchor = "left", yanchor = "middle"
    ),
    list(
      x = 1.01, y = 0.5, xref = "paper", yref = "paper",
      text = "?", showarrow = FALSE,
      font = list(size = 12, color = "white"),
      xanchor = "right", yanchor = "middle",
      bgcolor = "#1f77b4",
      bordercolor = "white",
      borderwidth = 1,
      width = 20, height = 20,
      opacity = 1
    ),
    # increase项
    list(
      x = 1.02, y = 0.4, xref = "paper", yref = "paper",
      text = "increase", showarrow = FALSE,
      xanchor = "left", yanchor = "middle"
    ),
    list(
      x = 1.01, y = 0.4, xref = "paper", yref = "paper",
      text = "+", showarrow = FALSE,
      font = list(size = 12, color = "white"),
      xanchor = "right", yanchor = "middle",
      bgcolor = "#ff7f0e",
      bordercolor = "white",
      borderwidth = 1,
      width = 20, height = 20,
      opacity = 1
    ),
    # decrease项
    list(
      x = 1.02, y = 0.3, xref = "paper", yref = "paper",
      text = "decrease", showarrow = FALSE,
      xanchor = "left", yanchor = "middle"
    ),
    list(
      x = 1.01, y = 0.3, xref = "paper", yref = "paper",
      text = "-", showarrow = FALSE,
      font = list(size = 12, color = "white"),
      xanchor = "right", yanchor = "middle",
      bgcolor = "#2ca02c",
      bordercolor = "white",
      borderwidth = 1,
      width = 20, height = 20,
      opacity = 1
    )
  ),
  # 调整右侧边距，给自定义图例留出空间
  margin = list(r = 80)
)

关键修改点 #

• 数据拆分：将符号与类别字段分离，分别控制图中显示的符号和图例文本内容
• 禁用默认图例：通过showlegend = FALSE关闭自动生成的图例，避免符号出现在标记后方
• 手动构建图例：用annotations自定义每个图例项，实现符号覆盖在彩色标记上方的效果，同时指定所需的图例文本
• 符号居中设置：主图中用textposition = "middle center"确保符号在标记正中央显示

内容的提问来源于stack exchange，提问作者Thierry